1. Field of the Invention
The invention relates to a method of photolithography, and more particularly to a method of photolithography with a nitrogen (N2) treatment after the deposition of an anti-reflective coating (ARC). While removing a photo-resist (PR) layer, oxidation of the ARC is suppressed, so that the alteration of the ARC quality is reduced.
2. Description of the Related Art.
As the integrated circuit (IC) device scales down, the required linewidth becomes narrower and narrower, and the resolution has to be increased. During photolithography, the wavelength of light source for exposure has to be shorter to meet the above requirements. However, as the wavelength of light source decreases, the reflection of silicon becomes more and more serious. The swing effect is thus more and more obvious. To avoid the reflection on the surface of a metal layer, to enhance the accuracy of exposure, and to control the linewidth precisely, an ARC, for example, a silicon-oxy-nitride (SiON), is formed on the surface of poly-silicon or aluminum alloy.
After patterning a poly-silicon layer, the photo-resist layer is removed. However, during deep ultra-violet(UV) photolithography, in case that abnormal exposure happens, the photo-resist layer has to be reworked. To remove the rework photo-resist layer, an oxygen (O2) plasma or sulfuric acid (H2SO4) and perhydrol (H2O2) is used. While removing the photo-resist layer by the oxygen plasma or sulfuric acid and perhydrol, the surface of the ARC is oxidized. The characteristics of the ARC, such as the refractive index (n), the decay coefficient (k), and the reflectivity, are altered to change the process condition.
In FIG. 1a to FIG. 1b, a conventional method to define a transistor in an IC is shown. Referring to FIG. 1a, on a substrate 100, a gate oxide layer 102, a poly-silicon layer 104, an ARC 106, and a photo-resist layer 108 are formed in sequence. The material of the ARC 106 includes silicon-oxy-nitride. Using a photo-mask 110, the photo-resist layer 108 is patterned to form a photo-resist mask 108a as shown in FIG. 1b. If the exposure is abnormal during the formation of photo-resist layer, the photo-resist layer 108 has to be removed and reworked
Referring to FIG. 1c, using the photo-resist mask 108a as a mask, the gate oxide layer 102, the poly-silicon layer 104, the ARC 106 are etched and patterned to form a gate 104a covered by an ARC 106a. 
Referring FIG. 1d, the reworked photo-resist mask 108a is removed by oxygen plasma or sulfuric acid.
Furthermore, the ARC 106a is removed. The ARC is removed for performing the subsequent salicide process without damaging the device. However, there is not a proper method to remove the ARC developed yet
A process flow of the above conventional method is shown as FIG. 3a. Referring to FIG. 4a, after the deposition of an ARC, the reflectivity 400 is about 18.7 In case of rework for photo-resist layer by H2SO4+H2O2, the reflectivity 402 is about 165. After removing the reworked photo-resist layer by O2 plasma, the reflectivity 404 is about 15.0.
It is therefore an object of the invention to provide a method of photolithography to avoid oxidation of the ARC surface during removing the reworked photo-resist layer. Therefore, alteration of the characteristics of the ARC is suppressed.
It is therefore another object of the invention to provide a method of photolithography. The ARC is removed without damaging the device.
To Achieve these objects and advantages, and in accordance with the purpose of the invention, as embodied and broadly described herein the invention is directed towards a method of photolithography. An anti-reflective coating is formed on a conductive layer. An nitrogen plasma treatment is performed. A photo-resist layer is formed and patterned on the anti-reflective coating. The conductive layer is defined. The photo-resist layer is removed.
To achieve these objects and advantages, and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention is directed towards another method of photolithography. Anti-reflective coating is formed on the conductive layer. An nitrogen plasma treatment is performed. A photo-resist layer is formed and patterned on the anti-reflective coating. The conductive layer is defined. The photo-resist layer is removed. The anti-reflective layer is removed by using phosphoric acid.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed